Carnosine, anserine, and other histidyl dipeptides occur in high concentrations in certain vertebrate tissues, and yet their function is unknown. We plan to study the metabolism of these compounds in an effort to elucidate their metabolic role. We have found an interesting histidine to N-acetyl histidine cycle in the lens and ocular fluid of the fish eye whose function may be the transport of divalent metals across a membrane against a gradient. Carnosine is closely related to N-acetyl histidine; it is hydrolyzed by the same enzyme, and may be a functional homologue of N-acetyl histidine. We plan to test this hypothesis by perfusing labelled compounds through various tissues. Any insights into the role of carnosine may suggest therapy for the treatment of the disease carnosinemia.